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Related Experiment Videos

pH-induced structural changes regulate histidine decarboxylase activity in Lactobacillus 30a.

E Schelp1, S Worley, A F Monzingo

  • 1Institute of Cellular and Molecular Biology, Department of Chemistry and Biochemistry, University of Texas, Austin, TX, 78712, USA.

Journal of Molecular Biology
|March 13, 2001
PubMed
Summary

Histidine decarboxylase (HDC) enzyme activity is controlled by pH. This study reveals how HDC unwinds at high pH and stabilizes at low pH, crucial for its function in Lactobacillus 30a.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • Histidine decarboxylase (HDC) from Lactobacillus 30a synthesizes histamine, vital for acid neutralization and cell growth.
  • HDC exhibits pH-dependent activity, being active at low pH and inactive at neutral to alkaline pH.

Purpose of the Study:

  • To elucidate the novel mechanism of pH-dependent regulation of HDC activity.
  • To determine the X-ray structure of HDC at pH 8 to understand its inactive state.

Main Methods:

  • X-ray crystallography to determine the structure of HDC at pH 8.
  • Structural analysis to compare HDC conformations at different pH values.

Main Results:

  • The X-ray structure at pH 8 revealed that helix B unwinds, disrupting the substrate binding pocket.

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  • At acidic pH, helix B is stabilized by protonation of specific aspartate residues (Asp198 and Asp53), acting as a proton trap.
  • pH significantly impacts the tertiary structure of HDC monomers, with minimal effect on quaternary structure, unlike hemoglobin.

    • Conclusions:

    • HDC's pH regulation mechanism involves conformational changes in tertiary structure, specifically helix B unwinding/stabilization.
    • This mechanism allows Lactobacillus 30a to control histamine production based on environmental acidity.
    • The pH-induced structural changes are distinct from those observed in hemoglobin regulation.